We don't have a scheme but you can install ATUM and take a look at these tables that will be created on your database:
The above are the tables created by ATUM. For the premium add-ons there are some others but, basically, all the tables you see on your db starting by atum_ are from ATUM.
And regarding your "custom fields for suppliers" question. ATUM does not support them but we have a filter in place, so you can change the parameters passed to the register_post_type function and to add support for custom fields easily. The filter you need to hook is atum/suppliers/post_type_args
I hope that helps.